1. Field of the Invention
The present invention relates to an endoscope provided with an insertion portion inserted into an object or a subject.
2. Description of the Related Art
In recent years, endoscopes have been widely used in a medical field and an industrial field. Endoscopes used in the medical field can observe organs in a body cavity by inserting an elongated insertion portion into the body cavity which is a subject and perform various types of treatment using a treatment instrument inserted into an insertion channel for the treatment instrument provided for the endoscope as required.
On the other hand, endoscopes used in the industrial field can observe damage and corrosion or the like of a region to be examined of an object or perform inspections of various types of treatment by inserting an elongated insertion portion of the endoscope into the object such as a jet engine and pipes at a factory or the like.
Normally, an insertion portion of an endoscope is provided, on its distal end in an insertion direction (hereinafter simply referred to as “distal end side”), with a bending portion which is bendable by 360° in directions combining four directions; upward, downward, leftward and rightward, by pivotably connecting a plurality of bending pieces along the insertion direction, or to be more specific, bending pieces arranged adjacent to each other in the insertion direction using rivets that constitute a plurality of rotation shafts, located at positions differing by 90° in a circumferential direction of the bending pieces.
Hereinafter, the bending in the configuration in which the bending pieces are pivotably connected together using rivets that constitute a plurality of rotation shafts, located at positions differing by 90° in a circumferential direction of the bending pieces is referred to as “two-axis bending.”
The bending portion is bendable in the aforementioned direction by one or a plurality of bending wires being pulled out of four bending wires inserted into the insertion portion according to bending operation by an operator. Hereinafter, the bending portion bent by the bending wires is referred to as “active bending portion.”
Furthermore, there is also a known configuration provided with a passive bending portion which cannot be bent by a bending operation of the operator, but is flexible and passively bendable when an external force is applied thereto, provided closer to the proximal end side in the insertion portion (hereinafter simply referred to as “proximal end side”) than the active bending portion.
For example, Japanese Patent Application Laid-Open Publication No. 2006-218231 discloses an endoscope having a configuration in which bending pieces are used in a passive bending portion and the radius of curvature of the passive bending portion is greater than the radius of curvature of an active bending portion.
The passive bending portion described in Japanese Patent Application Laid-Open Publication No. 2006-218231 conventionally also has the aforementioned configuration performing two-axis bending.
Here, FIG. 16 is a diagram schematically illustrating a distribution of maximum bending angles in the bending direction of a bending portion which performs two-axis bending. The “maximum bending angle” refers to a state in which peripheral edges of bending pieces adjacent to each other come into contact with each other and the bending thereof in the direction is regulated.
In FIG. 16, an arrow Y1 shows a maximum bending angle in an upward, downward, leftward or rightward direction, taking the upward direction as an example, an arrow Y2 shows a maximum bending angle in an intermediate direction between the upward and downward directions, and the leftward and rightward directions, taking the intermediate direction between the upward direction and leftward direction as an example. When a circle X shown by a dotted line indicates a track of an ideal maximum bending angle, the ideal for the maximum bending angle is that the maximum bending angle be the same, as illustrated with the circle X, no matter whether the bending portion is bent in the upward and downward directions or bent in the leftward and rightward directions or bent in an intermediate direction between the upward, downward, leftward and rightward directions (hereinafter referred to as “twist direction”), that is, no matter in which direction in 360° the bending portion is bent.
However, in the case of the two-axis bending, as shown in FIG. 16, it is geometrically known that the maximum bending angle of the bending in the twist direction is 1/cos(π/4)≈1.41 times (Y2=1.41Y1) with respect to the bending in the upward, downward, leftward and rightward directions as shown in FIG. 18, which will be described later, that is, an angle gap attributable to a difference in the maximum bending angle is generated 1.41 times.
That is, the actual track of the maximum bending of the bending portion that performs two-axis bending has a rectangular shape as shown by a solid line T1 shown in FIG. 16.
Moreover, it is necessary to reduce the difference in maximum bending angles by the bending direction, whether it is the active or passive bending portion. That is, as shown in FIG. 16, it is necessary to make the track of the maximum bending angle approximate to the circle X.
In view of the above-described circumstances, Japanese Patent Application Laid-Open Publication No. 2004-141366 discloses, as a solution to the problems of two-axis bending in the active bending portion, a configuration of an active bending portion which is bendable by 360° in directions combining four directions; upward, downward, leftward and rightward by pivotably connecting bending pieces arranged adjacently to each other in the insertion direction using rivets that constitute a plurality of rotation shafts, located at positions differing by 45° in a circumferential direction of the bending pieces.
Hereinafter, the bending in the configuration in which the bending pieces are pivotably connected together in upward, downward, leftward and rightward directions using rivets that constitute a plurality of rotation shafts, located at positions differing by 45° in a circumferential direction of the bending pieces is referred to as “four-axis bending.”
Here, FIG. 17 is a diagram schematically illustrating a distribution of maximum bending angles in the bending direction of the bending portion that performs four-axis bending and FIG. 18 is a diagram illustrating an angle gap with respect to the number of bending axes.
As shown in FIG. 17, when the active bending portion has a four-axis bending configuration as described in Japanese Patent Application Laid-Open Publication No. 2004-141366, in the case of four-axis bending, a maximum bending angle Y3 (represented by a UL direction in FIG. 17) in a direction intermediate between upward and downward directions, and leftward and rightward directions (UL direction, UR direction, DL direction and DR direction) of the twist directions is equal to a maximum bending angle Y1 in upward, downward, leftward and rightward directions (Y1=Y3), and as shown in FIG. 18, a maximum bending angle Y4 (represented by a twist direction between the UL direction and upward direction in FIG. 17) in the twist direction except the UL direction, UR direction, DL direction and DR direction is geometrically known to be 1/cos(π/8)≈1.08 times the maximum bending angle Y1 in the upward, downward, leftward and rightward directions and UL direction, UR direction, DL direction, DR direction (represented by the downward direction in FIG. 17) and Y3 (Y4=1.08Y1(Y3)), the actual track of the maximum bending becomes an octagonal shape shown by a solid line T2 shown in FIG. 17 and approximates to the circle X, and it thereby minimizes the difference in maximum bending angles by the bending direction.
As shown in FIG. 18, the greater the number of rivets connecting the bending pieces, that is, the greater the number of bending axes, the smaller is the difference in maximum bending angles by the bending direction, and it is clear that the angle gap due to the difference in maximum bending angles of a bending portion that performs n-axis bending is 1/cos(π/2n).
Here, FIG. 19 shows a diagram schematically illustrating the operation of raising the transverse colon using an endoscope having only an active bending portion, FIG. 20 shows a diagram schematically illustrating the operation of raising the transverse colon using an endoscope having an active bending portion and a passive bending portion, FIG. 21A shows a diagram schematically illustrating the operation of causing an endoscope having only an active bending portion to pass through the hepatic flexure of the intestine, FIG. 21B shows a diagram schematically illustrating the operation of causing an endoscope having an active bending portion and a passive bending portion to pass through the hepatic flexure of the intestine and FIG. 22 shows a diagram schematically illustrating the operation of causing an endoscope having an active bending portion and a passive bending portion to pass through the sigmoid colon of the intestine.
When performing the known operation of raising the transverse colon P using the insertion portion of an endoscope having only an active bending portion, which is normally used, it is a general practice as shown in FIG. 19 that a distal end portion 101 of an insertion portion 100 is made to pass through a descending portion N of the transverse colon P by bending an active bending portion 102 and the insertion portion is pulled back with the distal end portion 101 being hooked at the transverse colon P. After that, with the transverse colon P being raised and straightened, the insertion portion 100 is pushed in and made to move forward.
Moreover, it has been known that, as shown in FIG. 20, when an attempt is made to raise the transverse colon P using an insertion portion 200 in which a passive bending portion 203 is formed on the proximal end side of an active bending portion 202, since the passive bending portion 203 is formed to be flexible, the passive bending portion 203 is bent without raising the transverse colon P, and if the bending angle thereof becomes excessive, when the insertion portion is pulled back with the distal end portion 201 being hooked at the transverse colon, a force is applied to the distal end portion 201 in a direction opposite to the hooking direction, resulting in that the distal end portion 201 is twisted and the distal end portion 201 is unhooked.
Furthermore, as shown in FIG. 21A, also when the distal end portion 101 is made to pass through the hepatic flexure Q of the transverse colon P, in the case of a normal endoscope provided only with an active bending portion 102, the distal end portion 101 can be made to pass through the hepatic flexure Q when the distal end portion 101 has reached the flexural area of the hepatic flexure Q by rotating the insertion portion 100 counterclockwise from there. However, it has been known that, as shown in FIG. 21B, in the case of the endoscope provided with the passive bending portion 203, if the passive bending portion 203 is bent excessively, depending on the design, the distal end portion 201 does not reach the flexural area of the hepatic flexure Q.
Furthermore, it has been known that, as shown in FIG. 22, also when the insertion portion 200 passes through the sigmoid colon S, in the case of the endoscope provided with the passive bending portion 203, if the passive bending portion 203 is bent excessively, the force applying to the insertion portion 200 is inverted from S1 to S2.